Many available power protection devices, such as surge protection devices (SPDs) and hybrid filters, include an automatic switch circuit that disconnects AC power to the device output in response to various supply wiring fault and/or over voltage or under voltage conditions. Circuitry that detects over voltage and under voltage conditions requires nominal line voltage levels before AC power is passed to the device output and connected equipment. Line voltage conditions, such as swells and over voltages, can cause failure of certain power protection device components such as metal oxide varistors and other suppressor components. In addition, some equipment power supplies can be damaged by continuous over voltage conditions. Under voltage conditions can result from malfunctions in connected equipment such as short circuits, leading to potentially damaging or dangerous high currents within the power protection device or the connected equipment itself.
Despite the benefits of power protection devices that disconnect power to equipment in response to fault conditions such as over voltage and under voltage conditions, the resulting power disruptions can be inconvenient or problematic in many circumstances. To avoid frequent power interruptions, one solution would be to set the voltage levels at which power is disconnected well outside the normal operation range but still within levels tolerated by the equipment. However, this approach may result in frequent or chronic over voltage or under voltage conditions of lesser magnitude going undetected indefinitely, which may eventually lead to damage to the surge protection device or the connected equipment. Accordingly, there remains a need for a supply voltage monitoring system that provides over voltage and under voltage protection without causing frequent power disruptions while still providing adequate notification of lesser-magnitude over voltage and under voltage conditions that may indicate a problem condition within the system or with the connected equipment.